It is costly to deliver containers 2, such as Front Opening Unified Pods (FOUPs) and Standard Mechanical Interface (SMIF) pods, to processing tools 10 and load ports 12 in a semiconductor fabrication facility (fab). One method of delivering FOUPs and SMIF pods between processing tools is an Automated Material Handling System (AMHS).
An AMHS or transport system moves containers or cassettes of semiconductor wafers or flat panels (all referred to as containers herein) in a fab. Container movement within the fab may be within each tool bay (e.g., bays B1 and B2 in FIG. 1) (intrabay AMHS—generally comprises a transport system that moves containers within a bay and delivers containers to tool locations.) and between tool bays (interbay AMHS—generally comprises a transport system that moves containers along a main aisle that connects bays of processing tools.). Fabs often include stockers for storing containers. It is desirable to decrease delays in AMHS traffic by delivering containers directly from processing tool to processing tool as much as possible. Inadequate throughput capability in any part of the AMHS may cause other parts of the AMHS to have throughput that is below potential because the inadequate component is serially connected to the other parts.
Containers are often delivered to a stocker after a process step is completed and then later removed and delivered to another tool when the tool is ready. The limited throughput of a conventional stocker limits the entire throughput capacity of the systems that deliver and remove containers from a stocker. Thus, the overall throughput capacity of the AMHS is limited to the stocker throughput. For example, peak interbay transport throughput for a particular stocker may be 700 container or AMHS moves per hour. If this stocker is accessed by two AMHS for bidirectional transport, a potential peak interbay move rate of 1400 container moves per hour for that particular stocker may theoretically be achieved. If this stocker is further connected to another tool bay having an intrabay AMHS or other transport system with a 700 container moves per hour peak capacity, the peak moves rate for the stocker could reach up to 2100 container moves per hour. A conventional stocker can only make one container move every twenty seconds on average—limiting the peak throughput of the stocker to 180 container moves per hour, which is well below what may be required by the fab.
Even if only considering the throughput of the bay, and the stocker only handles container flow into the bay, the peak requirement could be 1400 moves per hour (700 moves per hour from interbay, 700 moves per hour to intrabay). This situation would cause the high potential throughput of the intrabay to be severely limited by the stocker.
Asyst Technologies, Inc. manufactures various high throughput systems, including the Direct Tool Loading system disclosed in U.S. patent application Ser. No. 11/064,880, entitled “Direct Loading Tool,” which is assigned to Asyst Technologies, Inc., and is incorporated by reference herein. The Direct Tool Loading system may also create this kind of throughput mismatch with conventional stockers. The Direct Tool Loading system is a floor-based container transport system (e.g., a container transport system that transports a container at an elevation equal to or lower than the processing tool loading height). Such a system requires a vertical transport process even if containers were delivered directly to the tools without first being stored in a stocker (different container delivery priorities). The combination of very high throughput stockers and vertical container transport systems are required to fully utilize the throughput potential of the Direct Load system. Conventional stocker limitations may not be readily apparent in some AMHS because the AMHS itself also has a limited throughput (not high throughput).
One type of AMHS or transport system is an overhead transport (OHT) system. In a conventional OHT system, an OHT vehicle, among other things, lowers a FOUP onto the kinematic plate of the load port at approximately 900 mm height from the fabrication facility floor. An OHT system uses sophisticated ceiling mounted tracks and cable hoist vehicles to deliver FOUPs to these load ports. The combination of horizontal moves, cable hoist extensions, and unidirectional operation, must be coordinated for transporting FOUPs quickly between processing tools. For optimum efficieny within an OHT system. an OHT vehicle must be available at the instant when a processing tool needs to be loaded or unloaded. This is not always possible.
Other non-conveyor AMHS or transport systems that use a vehicle to move containers throughout the fab (e.g., automated guided vehicle (AGV) system, rail guided vehicle (RGV) systems, overhead shuttle (OHS) systems) require the AMHS scheduling system to manage the movement and availability of empty vehicles as well as the loaded vehicles that are making deliveries. This heavy burden on the scheduling system often results in container pick-up delays because empty vehicles are directed to the pick-up location and added traffic congestion results due to non-productive empty vehicle movement. Similar delays occur with OHT vehicles. The OHT vehicle may take, for example, fifteen seconds to complete the container pick-up or drop-off step, and during this pick-up/drop-off time, container traffic is blocked at that location of the AMHS. These factors combine to limit vehicle based intrabay AMHS to, for example, 100-200 moves per hour in many cases. This does not present a large mismatch with conventional stocker capabilities. However, many tool bays require much higher throughput that cannot be met with the conventional stocker/OHT architecture.
Asyst's Direct Tool Loading system provides an AMHS solution for high throughput intrabay tool delivery capability. The Direct Tool Loading system provides several advantages for throughput: extension of high throughput conveyor AMHS directly to the tool, and, due to individual load port conveyor load/unload mechanisms, highly parallel conveyor interfaces. At any given time, many containers may be in the process of being dropped off onto the conveyor or picked-up from the conveyor with no mutual interference. To fully utilize its throughput potential, the AMHS requires a combination of high throughput stockers and vertical transport systems that efficiently connects to the interbay AMHS in flexible configurations that meet varying fab configurations.
Therefore, there is a need for improved high-throughput container transport systems and storage capabilities within a fab. The present invention provides such a system.